1. Field of the Invention
The present invention relates generally to grinding apparatus. More particularly, the invention concerns glass grinding apparatus, and especially table top grinders for use by hobbyists in the fabrication of glass artwork and decorative glass products.
2. Description of Prior Art
By way of background, there is a wide variety of grinding apparatus for shaping and/or surfacing many different kinds of materials. Of particular interest herein are table-top grinders of the type used by glass hobbyists and the like. Commonly assigned U.S. Pat. No. 6,416,394, entitled “Planer/Grinder For Glass,” whose contents are incorporated herein by this reference, exemplifies such equipment. The typical glass grinding apparatus includes a cylindrical grinding bit mounted on a motor-driven shaft that spins above a horizontal work piece platform. The grinding bit can be formed with a surface coating of diamonds or other abrasive particles capable of grinding, sanding or polishing glass. A glass work piece that is to be shaped or otherwise treated is placed on the platform and advanced until its edge contacts the grinding bit. By maneuvering the work piece relative to the grinding bit, material can be selectively removed from the work piece edge to create a desired shape and/or surface treatment.
Because the grinding process generates both heat and grinding debris, a fluid such as water is typically used to cool and wash the grinding bit. In the typical grinder design, a sponge is situated to continually irrigate the grinding bit with the fluid. A reservoir of irrigation fluid is situated below the work piece platform, in a tank or tray. The lower end of the sponge is in contact with the irrigation fluid and draws it upwardly to the grinding bit. In other grinder designs, a spray nozzle is situated to disperse irrigation fluid onto the grinding bit, and a pump is used to draw the fluid from the reservoir. After application of the irrigation fluid to the grinding bit, the fluid is collected and returned to the reservoir via a plurality of passageways formed in the work piece platform. In particular, the work piece platform is commonly constructed as a lattice grating that freely passes the irrigation fluid below the grating to the tank or tray that holds the irrigation fluid.
There are several problems associated with the use of irrigation fluids to aid the grinding operation. First, the fluid tends to spray outwardly from the grinding bit in a radial direction, particularly away from the back side of the grinding bit that is not in contact with the work piece. Second, the grinding debris combines with the irrigation fluid to form a sludge that collects on the surface of the grinding bit, thereby reducing its effectiveness as a grinding tool.
To address the spray control problem, splash guards have been proposed that contain the fluid spray within a limited area. According to one design, the splash guard comprises a folding screen made from plastic-coated cardboard or the like that is stood upright behind the grinding apparatus on a table or other surface. The screen is about the size of a conventional three-ring notebook binder and has two or more panels that can be unfolded into the operational position. The primary disadvantage of this type of splash guard is that the fluid it catches has nowhere to go except downwardly onto the surface that supports the screen. This requires messy clean up of the accumulated fluid. Moreover, the screen can block a large work piece as it is being maneuvered around the grinding bit. According to another design, the splash guard comprises a rubber strip member that fits onto a vertical peg located behind the grinding bit on the work piece platform. When mounted on the peg, the strip rises about an inch above the work piece platform and extends horizontally and forwardly from each side of the peg for several inches. The strip thus forms, generally speaking, a “V” shape when viewed in plan. Although this type of splash guard is situated so that the fluid it catches will be returned to the fluid reservoir, the guard is not tall enough vertically or wide enough horizontally to catch much fluid. Moreover, when the guard is contacted by a large work piece being maneuvered around the grinding bit, a portion of the guard will bend rearwardly (when viewed in plan) so as to give way to the work piece. This has the effect of temporarily reducing the amount of the splash protection during the time that the guard is displaced.
To address the sludge removal problem, the sponge used to irrigate the grinding bit is positioned so that its upper end applies contacting pressure against the bit. This has the effect of wiping sludge from the grinding bit as the fluid is applied. However, the sponge quickly becomes clogged with sludge, which not only prevents it from effectively removing additional sludge, but also clogs the fluid passageways of the sponge such that the flow of irrigation fluid to the grinding bit is reduced. Frequent sponge cleaning and/or replacement are thus required. Moreover, the sponge is not able to completely remove sludge from all of the interstitial cracks and crevices that lie between the abrasive particles on the grinding bit surface. The interstitial sludge will build up until it appears to the naked eye that the grinding bit is worn down to an overly smooth condition. This can result in premature replacement of the grinding bit when in fact the bit actually has sufficient grinding capacity that could be realized if the sludge were removed.
Accordingly, there is presently a need for improvement in the way that irrigation fluids are handled in grinding apparatus. What is required in particular is a grinding apparatus design wherein irrigation fluid spray is effectively contained and returned to a source location without messy clean up, and wherein the effective removal of grinding bit sludge is achieved.